1 пример наверное так:
(1/1-x) -3/(1-x)(1+x+x^2) = (1+x+x^2-3)/(1-x)(1+x+x^2) = (x^2+x-2)/(1-x)(1+x+x^2)=(1-x)(x-2x-2)/(1-x)(1+x+x^2)=(x-2x-2)/(1+x+x^2)=-1